It is well recognized that pressure balanced-type gate valves have been in use for many years. The pressure balancing concept is employed to prevent the development of pressure induced forces that would retard the operability of the valve mechanism. In most gate valves, the fluid pressure controlled by the valve acts upon the cross-sectional area defined by the valve stem and develops a force acting upon the valve stem that tends to move the gate element toward one of its extreme positions of movement. This force can be sufficiently great, depending upon the pressure within the valve and cross-sectional area of the valve stem, that the actuator system needed for controlling the valve must be of quite heavy duty and expensive nature. When pressure induced forces are extremely great and the valve mechanism is of the manually operated type, it can be extremely difficult for personnel to operate the valve.
By providing a pressure balancing stem connected to the gate element and extending through the valve body with one extremity thereof exposed to the atmosphere, fluid pressure acting on the cross-sectional area of the pressure balancing stem will develop a pressure induced force that counter-balances the force applied to the valve stem. The gate element may therefore be operated by simply overcoming the frictional forces of the gate, valve seats and packings. Even while maintained under extremely high pressure conditions, pressure balanced valves may be readily opened and closed while applying only mininal forces during such opening and closing movement.
Pressure balanced valves generally include a pressure balancing system wherein the pressure balancing stem is exposed to the atmosphere. In the event valves of this nature are employed in underwater service, it is possible that marine growth and other normal conditions of a marine environment might foul the valve mechanism by means of the pressure balancing opening. Pressure balanced valves are therefore seldom utilized in marine environment unless provided with an oil/water interface system or some other protective mechanism to prevent sea water from coming into contact with the pressure balancing portion of the valve mechanism. It is desirable, therefore, to provide a pressure balanced gate valve mechanism incorporating a pressure balancing system that is not exposed to the hazards of the environment within which it might be located.
Valve mechanisms, including pressure balanced valves mechanisms, are at times provided with back-face seating arrangements so as to establish a seal between the valve stem and bonnet structure of the valve mechanism when desired. For example, should it be necessary to replace the packing assembly of a gate valve while the valve structure is maintained under pressure and in service, a sealing surface provided on the valve stem may be brought into metal-to-metal sealing contact with an appropriate mating seat formed within the bonnet structure. With this metal-to-metal seal established, the packing assembly can be replaced so as to prevent any leakage between the valve stem and bonnet. It is desirable to provide a back-face seating system for the valve mechanism including back-face seating between the valve stem and bonnet structure and between the pressure balancing stem and the valve body structure. It is also desirable to provide stop means for limiting travel of the gate element such that in the open position the port of the gate element is precisely registered with the flow passages of the valve so as to provide a through conduit type valve structure that can accomodate passage of production tools and equipment that might be passed through the valve mechanism. It is also desirable to provide a back face seating arrangement whereby the valve actuator mechanism may be immobilized and back-face seating can be accomplished regardless of the position of the gate element within the valve mechanism.
Where safety override systems are employed, such as are utilized to move the gate element to a predetermined position responsive to the occurence of a condition such as failure of the power system of the valve, for example, it may be desirable to move the gate element to the open or closed position. It is desirable therefore to provide a gate element that is positionable within the valve mechanism such that the gate is either open or closed responsive to movement thereof to the predetermined position by the safety override system. It is therefore desirable to provide a gate element that is reversible to selectively position the port at the open or closed position when energized by the safety override system.
At times, even when manual actuators are employed, the actuator system may become inoperative due to mechanical problems. It is desirable, therefore, to provide means for imparting controlling movement to the gate element to move the gate to a preselected position by means of a hydraulic auxiliary actuator system.
In many cases, valves are provided for controlling flow lines and the valves are provided with a particular kind of actuating system. In the event it is desirable to provide the valve mechanism with a different kind of actuator system, it may be necessary to disconnect the valve from the line and transport it to a repair facility in order that it can be adapted for receiving a different kind of actuator. It is desirable to provide a valve mechanism that is adapted to accept a wide range of actuator systems including manual, mechanical, hydraulic and pneumatic systems and to provide for field interchange of valve actuator systems without necessitating removal of the valve from the line. It is also desirable to provide valve actuator systems that can be simply and easily installed and removed without necessitating disconnection of hydraulic or pneumatic supply lines in the event the actuator system is provided for pneumatic or hydraulic actuation.
In view of the foregoing, it is an important feature of the present invention to provide a valve mechanism incorporating a standard actuator connection system that effectively promotes connection of any one of several different types of valve actuators to the valve mechanism and to accomplish removal and replacement of actuator systems while the valve is maintained in service and under pressure.
It is another feature of the present invention to provide a novel balanced stem type gate valve mechanism having a pneumatic or hydraulic actuator system therefor wherein the actuator system may be removed from the valve mechanism and replaced without requiring disconnection of hydraulic or pneumatic control lines.
It is another feature of the present invention to provide a novel gate valve mechanism that is adapted for actuation by a number of different types of actuator systems and wherein a hydraulic override system is provided enabling the gate of the valve mechanism to be moved to a predetermined position by a portable hydraulic actuator system.
Among the several features of the present invention is noted the contemplation of a novel pressure balanced gate valve mechanism incorporating back-face seal systems for both the actuating stem and pressure balancing stem to enable replacement of packings while the valve is in service and under pressure.
It is also a feature of the present invention to provide a novel pressure balanced gate valve mechanism wherein elastomeric seals are utilized to enhance the sealing ability of metal-to-metal back-face seals with which the valve mechanism is provided.
Another feature of the present invention contemplates the provision of a novel pressure balanced gate valve mechanism incorporating a reversible gate for positioning of the gate port either in open or closed position responsive to automatic movement of the gate to a preselected position by a safety override system.
It is another feature of the present invention to provide a novel pressure balanced gate valve mechanism that is capable of establishing back-face sealing regardless of the initial position of the gate and valve stem elements at the initiation of movement toward the back-face sealing position.
It is another important feature of the present invention to provide a novel pressure balanced gate valve mechanism incorporating a closed loop fluid interchange system that allows a pressure balanced condition to be established and prevents venting of the pressure balancing stem or valve stem to the atmosphere.
Other and further objects advantages and features of the present invention will become apparent to one skilled in the art upon consideration of this entire disclosure. The form of the invention, which will now be described in detail, illustrates the general principles of the invention but it is to be understood that this detailed description is not to be taken as limiting the scope of the present invention.